Method of accelerating the hardening of concrete slabs



J. C- KELLY July 20, 1954 METHOD OF ACCELERATING THE HARDENING OFCONCRETE SLABS Filed May 23, 1952 INVENTOR v9.56 (i jfZZgj, BY

ATTORNEY Patented July 20, 1954 UNITED IHETHOD OF ACCELERATING THEHARDEN- ING OF CONCRETE SLABS Joseph 0. Kelly, Linwood, N. J.

Application May 23, 1952, Serial No. 289,514

4 Claims. 1

My invention relates to a new and useful im provement in a method ofaccelerating the hardening of concrete slabs.

As is well known to those skilled in the art, when laying floors orconcrete slabs of the monolith type, the hardening of the concrete isrelatively slow, and especially if the concrete is poured in the springor fall when the temperature is around forty or fifty degrees (40 or50).

It often happens that after the concrete is poured, as for instance inthe afternoon, the temperature will fall say to forty degrees (40) andthe concrete will have to dry or harden a number of hours before theworkmen can trowel or smooth the surface. This necessitates a. needlessWaste of time.

One of the objects of the present invention, therefore, is to provide amethod wherein even if the temperature is just slightly above freezing,the concrete may be poured; and by providing a number of relativelylarge electrodes, say from twenty to thirty inches square (20" to 30")and positioned in a row, and connecting the reinforcing metal in theconcrete slab to form the other electrode, and then passing electriccurrent therethrough, I can hasten the hardening of the concrete so thatin from twelve to thirteen minutes, the workmen can walk or kneel on thestrip so hardened and trowel or surface the same while the next strip isbeing hardened.

Still another object of the invention is to provide a number of copperelectrodes, each of which consists of a sheet of copper nailed orsecured to a back of relatively stiff material, such as compo-board, orplaster board, or any other form of board, to provide sufficientrigidity for the plate; and then to drill a number of holes therein, orin other words, perforate the electrode, that is, the back and thecopper sheet so that as the excess moisture arises from the cencretethat is being heated, the steam may pass through the electrode and thushasten the time of the hardening.

Still another object of the invention is to provide a method wherein anumber of these electrodes can be placed in a row to thus heat theconcrete, a strip or row at a time, until the entire slab has been soheated.

With these and other objects in view, which will be described as theapplication proceeds, reference is now made to the drawings, showing howmy method is employed to accelerate the hardening of the concrete.

Fig. 1 is a perspective, showing a monolith floor with a plurality ofelectrodes in place, the electric circuit being diagrammatically shown,and

Fig. 2 is a fragmentary, sectional View, showing a portion of the slab,one of the portable electrodes and the metal reinforcement.

At the outset it might be mentioned that the method primarily consistsin passing an alternating current through the plastic mass, wherein themetal reinforcing rods or wire mesh form the one electrode, and aplurality of copper plates also connected to the alternating current areplaced in position on the concrete to form the other electrode, so thatas the current passes through the mass, it will cause the temperature torise to approximately one hundred ninety or two hundred degrees or 200)and thus accelerate the hardening of the concrete and drive out themoisture and steam which may escape through the perforations in theupper cop per electrodes.

Referring now to Fig. i, there is shown, in perspective, a. monolithslab of concrete l. I have not shown any confining walls or molds asthey may be of any conventional type, as it will be understood that theconcrete may be used to form floors in houses, basements, garages, orany other concrete surface.

Still referring to Fig. 1, there is shown the ends 2 of the metalreinforcements, which are also of the conventional type used in thelaying of concrete slabs. Where the slab is four inches or under, onlyone set of concrete reinforcing rods or mesh is used; but, if the slabis over four inches, the conventional method is to use another set, at alevel spaced from the first set.

The present method is adapted to accelerate the hardening of concreteslabs that are up to three or four hundred feet square (300 or 400 sq.ft.).

Referring now to Figs. 1 and 2 for the moment, there is shown aplurality of copper portable electrodes 3, and as they are all similar,a description of one is a description of the others.

This electrode 3 consists of a relatively thin copper plate 4 which isnailed to a board 5 to form a rigid plate; and as may be seen in Fig. 2,the copper plate 4 extends up and over the upper edges of the board 5 asat 6, around the four sides, and is held in place by the nails 1.

As heretofore mentioned, the back 5 may be of wood or composition boardor plaster board, and after the copper sheet is well nailed in place, aplurality of holes 8 are drilled through the entire electrode 3 so thatthe excess moisture may escape from the concrete as the current ispassed back and forth through the mass.

At one side of the electrode 3 there may be an electric socket 9 for thesake of convenience; and as shown in Fig. 1, this socket 9 will beelectrically connected by the wire H] to the socket l 1., which in turnis fastened to one of the inlet leads 12. The other conductor or thesupply of current is-carried by the wire i3 which at its far end M isconnected to the aforementioned reinforcing rods 2 which are imbedded inthe plastic mass.

The other electrodes are similarly connected by the conductors i5, i8and ll, all of which are in parallel. Thus, any of the conductors to thesockets in the electrodes may be quickly connected or disconnected.

The electrodes 3 are relatively light in Weight and it will beunderstood that the workmen can easily move them from one position toanother.

The electrodes may be of any desired size, and those about twenty inchessquare have proved very efficient in service.

There will be about seventy or eighty perforations or holes 8 in theplate to thus let the excess rising moisture escape from the concrete asthe same is being hardened by the heat from the alternating current.

Referring to Fig. 1 again for the moment, I have shown the fourelectrodes 3 in what might be termed a row A, and after about twelve tothirteen minutes of the alternating current passing through theconcrete, the excess moisture will have all passed out through theperforations 8, and the concrete in the row will then be hard enough forworkmen to walk on the same and trowel or surface the row A. The currentwill then be turned off and the workrnen will move the electrodes 3 overto what might be termed the strip B; and while the concrete is beingtroweled in strip A, it will be hardening and drying in strip B. Theprocedure may then be repeated in strip 0, etc.

The current necessary is the ordinary house current of one hundred tenvolts (110 volts) and I have found that thirty amperes amps.) willprovide sufficient current to accelerate the hardening of the concretein from twelve to thirteen minutes.

Thus, it will be seen that the trowelling of the upper surface can takeplace within a relatively few minutes after the concrete is poured,which is not possible when the concrete is laid in relati'vely coldweather. Thus, many hours may be saved in the hardening and trowellingof the concrete.

The current flowing through the concrete row preserves a uniformtemperature throughout the entire row.

It will be understood that I can use any number of these portableelectrodes 3 as desired, but I have found that at one time, the methodshould be used on a slab not over four hundred feet (400) square.

I am aware that it is old to pass an alternating electric currentthrough a plastic mass (concrete) in which there is water, as set forthin Patent No. 1,808,762, of June 9, 1931, to Albert Brund and HelgeB'ohlin; but I am not aware of a method of laying a concrete monolithslab wherein perforated portable electrodes may be arranged in rows toheat the concrete so that the concrete may be trowelled in a relativelyshort time, and, as the trowelling proceeds, an adjacent row of theconcrete may be hardened.

The method has proved extremely efficient and permits the laying andtrowelling of the concrete in relatively cool weather without anywaiting for the concrete to harden sufficiently to trowel or surface thesame.

Having thus described my invention, what I claim is new and desire tosecure by Letters Patent is:

1. The method of accelerating the hardening of concrete monoliths whichhave reinforcing metal therein, which consists in connecting one lead ofan alternating current to said metal reinforcing within the monolith,placing a plural-- ity of perforated reinforced copper plates in a rowon top of said monolith, passing an alternating current through themetal reinforcing, copper plates and concrete, the excess moisture fromthe heated concrete passing up through the perforations in the copperplates, shutting off the current when the moisture stops passing throughthe perforations in the copper plates, trowelling the surface sotreated, moving the copper plates across the slab to accelerate thehardening of an adjacent row or strip while the first row is beingtrowelled, and continuing the method until the entire slab has beenhardened.

2. The method of accelerating the hardening of a metal reinforcedconcrete slab, which consists in connecting the metal reinforcing to anelectric current conductor to form one electrode, placing a number ofcopper electrodes, in the form of relatively large plates, in a row ontop of the concrete, connecting them to the other lead of thealternating current, said copper electrodes provided with a plurality ofperforations for the escape of excess moisture, running the currentthrough said metal reinforcing, copper electrodes and concrete forsubstantially twelve to thirteen minutes, moving the said copperelectrodes to form another row, trowelling the concrete of the firstrow, and repeating the process until the entire slab has been hardenedand troweled.

3. The method of accelerating the hardening of a freshly poured metalreinforced concrete slab, which consists in connecting the metalreinforcing to a conductor of an alternating electric current to formone electrode, placing a number of copper electrodes in the form ofplates substantially twenty inches square in a row on top of theconcrete slab, connecting them to the other conductor of the alternatingcurrent, said copper electrodes provided with a plurality ofperforations for the escape of excess moisture, running a current of onehundred ten volts and thirty amperes through said electrodes andconcrete for substantially twelve to thirteen minutes, moving the saidcopper electrodes to form another row, and repeating the process untilthe entire slab has been hardened.

4. The method of accelerating the hardening and finishing of a metalreinforced concrete slab, which consists in connecting the metalreinforcing to one conductor of an alternating electric current to thusform one electrode, placing a number of copper electrodes in the form ofperforated plates in a row on top of the concrete, connecting them tothe other lead of the alternating current, said copper electrodesprovided with a plurality of perforations for the escape of excessmoisture, running an alternating current of one hundred ten volts andthirty amperes through said electrodes and concrete until the excessmoisture stops passing through the perforations in the said copperelectrodes, moving the copper electrodes to form an adjacent row orstrip, trowelling the first row while the second row is being treated,and repeating the process until the entire slab has been hardened andtrowelled.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 508,112 Miller Nov. 7, 1893 661,443 Coulon Nov. 6, 19001,098,436 Hadaway June 2, 1914 1,808,762 Brund et a1 June 9, 19312,152,365 Smith Mar. 28, 1939 2,289,248 Davis July 7, 1942 2,347,324Johnson Apr. 25, 1944 2,378,142 Hunter June 12, 1945 2,500,866 RamsayMar. 14, 1950

